The present application is directed to methods for forming a toner image within an image forming device and, more particularly, to methods for controlling transitions between color printing and black-only printing.
Color image forming devices contain two or more cartridges, each of which transfers a different color of toner to a media sheet as required to produce a full color copy of a toner image. One common image forming device includes four separate cartridges for each of yellow, magenta, cyan, and black colors. Image formation for each cartridge includes moving the toner from a reservoir to a developer member, from the developer member to a photoconductive member, and from the photoconductive member to either a media sheet or an intermediate member. The toner images from each cartridge are formed on the media sheet in an overlapping arrangement that ultimately forms the final composite toner image.
In many devices, each cartridge is driven during image formation, even when one or more colors are not being used for the specific print job. When the cartridge is driven, the developer member forces toner through multiple compressive nips, even when the developer member is not actually transferring toner. Repeatedly passing toner through the compressive nips inflicts some level of damage to the toner. Worn or damaged toner particles may result in poor transfer to the photoconductive member, then poor transfer to the media sheet or intermediate member. Thus, each time a given particle of toner passes through a nip, the likelihood of that particle responding to the image formation process decreases.
Methods to reduce or eliminate undue wear on the toner would result in better overall efficiency of the image forming device. This in turn would increase the amount of toner available for transfer to the media sheets, and would decrease the amount of wasted toner.